Determination of zinc by square-wave adsorptive stripping voltammetry using alizarin as a chelating agent

The adsorptive collection of zinc(II) complex with alizarin ligand, coupled with the square-wave voltammetric technique at the hanging mercury drop electrode, yields a very sensitive electroanalytical procedure for the determination of zinc. The optimized experimental conditions include: supporting electrolyte (carbonate buffer), pH (11), alizarin concentration (1 × 10−6 mol l−1), accumulation time (60 s), accumulation potential (−0.1 V), scan rate (700 mV s−1), pulse amplitude (0.06 V) and SW frequency (80 Hz). The monitored stripping voltammetric current was linear over the range of 5 × 10−8 – 4 × 10−7 mol l−1 and the detection limit was 1 × 10−8 mol l−1. The relative standard deviation was calculated as 1.3% (n = 10) for 1 × 10−8 mol l−1 Zn(II) and the obtained electrochemical signal was stabile for up to 60 min. Possible interferences by either co-existing metal ions or other chelating agents were also investigated. The applicability of the proposed SW-AdSV method to the analysis of foodstuff was assessed by the determination of zinc content in instant coffee samples. The accuracy of the obtained voltammetric analytical results was validated by comparing with that obtained by atomic absorption spectrometric method and conducting the necessary statistical evaluation.